Lubricant for internal combustion engines



Patented Mar. 25, 1941 LUBRICAN '1 FOR INTERNAL COMBUSTION.

' ENGINES Norbert F. Toussaint, Philadelphia, Hannibal J. R. Gaspari,Blawnox, and Henry A. Ambrose, Penn Township, Allegheny County, P a.,assignors to Gulf Research 8: Development Company, Pittsburgh, Pa., acorporation of Delaware No Drawing. Application January 17, 1939, SerialNo. 251,434

4 Claims. (Cl; 252-35) Our invention relates to improved lubricants foruse in internal combustion engines, such as automotive engines, aviationengines and Diesel-type engines.

Progress in the design of internal combustion engines of all kinds tendsto impose more and more severe burdens upon lubricants employed therein.The general tendency is always in the direction of higher performanceand increased horse-power per unit of weight. This tends to makelubrication more difficult and frequently to introduce entirely newproblems into the preparation and selection of lubricants for aparticular engine or typeof engine. Individual lubricating problemsarise with reference to different points in the engine. A satisfactorysolution of any one of these individual problems alone is sometimesdifficult enough in itself but becomes further complicated when, as isfrequently the case, it is found that improvement of a lubricant withrespect to one problem may make another problem in the same engine moreserious.

Thus, it has been found that a lubricant giving generally good crankcaseperformance in a particular engine may not be entirely satisfactory forlubrication of the cylinder walls, piston and piston rings of the sameengine, and vice versa.-

That is because entirely different physical conditions are encounteredin the cylinders than are encountered in the crankcase. Temperatures,rubbing'speeds, unit pressures, and other factors vary considerably atdifferent points in any internal combustion engine. Nevertheless thedesign of internal combustion engines is such that a single lubricant isrequired,'and that lubricant must give satisfactory service under thevariety of conditions encountered in each engine.

To illustrate this more fully, a good crankcase lubricant should be asfree as possible from sludging tendencies, and its viscosity change overa given temperature variation should be a minimum, i. e. it should havea high viscosity index. Parafiinic petroleum oils, such as thoseobtained from Pennsylvania crudes, possess these characteristics to agreater extent than do lubricating oils made by ordinary refiningmethods from less, highly paraflinic crudes, such as Coastal andMid-Continent crudes. During the past'decade or so, greatstrides havebeen made in refining methods, so that it is now possible to producefrom the less highly parafiinic crudes lubricating oils which approachPennsylvania lubricating oils in general performance characteristics.Even Pennsylvania oils are refined to increase their purityand'parafllnicity. One of the .best general automotive lubricants in usetoday is made from Pennsylvania crude stock, drastically refined bymeans of aluminum chloride; the resultant lubricating oil, without anysynthetic additions, is approached in value only by some oils which havebeen carefully refined and then improved. by the addition of various andmore or less synthetic improvement agents.

In any event, the general crankcase performance of such oils isexcellent and they command a justified premium on that account.

Neverthelesaas might be expected, the fact that these oils possessexcellent crankcase performance characteristics does not mean that theseoils are not susceptible to improvement with respect to performanceunder special conditions and at particular points in internal combustionengines Where the conditions are radically different from thoseencountered in the crankcase. Moreover, in improving such highly refinedoils, withrespect to their performance characteristics under suchparticular conditions, problems are sometimes encountered which, forvarious reasons, are more diflicult to solve than would be true of lesshighly refined oils.

That has been true, for example, with respect to the corrosion, ofcertain types of corrosionvsensitive metal bearing alloys, of which thesocalled cadmium-silver, copper-lead" and cadmium-nickel bearing alloysconstitute examples. In proper engine designs these bearings should givelittle or no trouble with any oil, but'in occasional instances thedesign of the engine may be such (particularly where excessive bearingtemperatures are maintained) that we are confronted with the apparentparadox that the best oils do not give the best over-all results and mayeven be undesirable under particular conditions. It is generally knownthat the more highly refined oils are, for some reason,

. occasionally more likely to cause more corrosion v of sensitive alloybearings at high temperatures. than is true of the less highly refinedoils.

Our invention is not primarily concerned with the solution of theproblem of lubricating sensitlve metal-alloy bearings, and the foregoingis mentioned simply for the purpose of illustrating the complexity ofthe problem of producing a satisfactory lubricant which, in use, mustencounter a considerable variety of specific lubricating conditions.

It might at first be thought that the simple remedy would be to reducethe degree of refining and to go back to cheaper oils. That can be done.however, only by sacrificing general crankcase performancecharacteristics of the highly refined oils, which is undesirable. And ithas been found that this particular problem can be met satisfactorilyand without such a sacrifice, by the use of small quantities of additionagents 7 having a specific and beneficial effect upon the particularproblem referred to but which do not impair the primary physicalcharacteristics and the general performance characteristics of thelubricant. Obviously, that is the way the problem should be solved. v I

Our invention is, however, more particularly concerned with the problemsencountered in upper cylinder lubrication of internal combustionengines. The difficulties encountered in the cylinders manifestthemselves most apparently, from the standpoint of the user, in what isgenerally known as ring-sticking. No internal combustion engines of theordinary type are entirely free from this tendency, but it isencountered more frequently and more seriously in connection withheavy-duty engines, such as Diesel-typo and aviation engines. Thedisadvantages of a lubricant which tends to cause the piston rings tobecome stuck are too obvious to require discussion. Suffice it to saythat a satisfactory lubricant should permit an engine to run at highspeed and under high load for a long period of time without anyappreciable ring-sticking tendency, other than that attributable tomechanical features of the engine design rather than to any failure onthe part of the lubricant.

The problem of ring-sticking is extraordinarily complex. That this wouldnecessarily be the case is evident from the fact that combustion istaking place at or adjacent to the points requiring lubrication.Temperatures tend to be very high, and there is a pronounced tendencyfor the lubricating oil to be burned or oxidized or otherwise removedfrom the metallic surfaces in moving contact with each other. Years willprobably pass and much intensive research will be done before those inthe art are able to specify with any degreeof certainty the fundamentalcause or causes underlying the ring-sticking tendencies andcharacteristics of petroleum lubricants.

It has been observed that ring-sticking is usually accompanied by theaccretion of more or less solid deposits around the rings and on theadjacent metal surfaces being lubricated. These deposits may take theform of carbon, or heavy hydrocarbons (generally referred to as gum,although not necessarily analogous to the gums formed in crackedgasoline distillates), or they may appear as lacquer-like deposits.These three types of deposits result from various types of chemicalactions and are not necessarily interrelated except .for the fact thatthey are solid in character; for that reason their accretion tends toprevent or interfere with normalaction of the piston rings. No oils areentirely free from these tendencies, but some oils, for no readilyapparent reason, are better than others, and

' oils which may produce generally equivalent results may actually do sothrough the mechanism of entirely different chemical reactions/ Thus ithas been observed that in the operation of Diesel engines, usinglubricants derived from Coastal crud'es, ring-sticking tendencies tendto show up more rapidly and more seriously with respect to the bottompiston rings of a particular engine, whereas there is a tendency for thetop rings to stick first when the 'same engine is lubricated withparafiin base oils. .Itjwould appear that the phenomenon is not'onlyconnected with temperature but also with the chemical composition of theoil.

' On .the other hand, a lubricating oil which tends to undergo excessivesludging in the crankcase may give excellent performance characteristicswith respect to ring-sticking. Such an oil, even when employed in aheavy-duty Diesel engine, may leave the piston ring assemblagesrelatively clean and-clear. A better oil, however, should give goodover-all performance characteristics. It should not be necessary tosacrifice desirable crankcase performance characteristics in order toachieve freedom from ring-sticking and the deposition of gum and lacquerin the upper cylinders.

We have found that in general the deposition of gum in the cylinders isrelated in some manner to the volatility of the lubricating oil, and.that as between two oils of the same viscosity, one of which is astraight distillate (particularly one having a low end boiling point)and the other is a residual oil or a. blend containing a residual oil,the latter will be found to cause more gum formation and hence morering-sticking than will be true of the former. It is not, however,possible to overcome the problem fully by simply employing a distillateoil or selecting an oil of a given volatility.

Others have suggested, prior to our invention, that certain metallicsoaps will stabilize petroleum lubricating oils against oxidation,polymerization or a combination thereof, which would ordinarily tend toresult in the deposition of carbonaceous material or sludge and in anun-' desirable change of color. The naphthenates of manganese, cobalt,lead and zinc have all been suggested as antioxidants for lubricatingoils.

Whether-or not such naphthenates are actually effective antioxidantsunder conditions of use in internal combustion engines is, however, nota simple question to answer. The action of naphthenates in preventing orpromoting oxidation appears to be a function of temperature to a veryconsiderable extent. At atmospheric tempera tures an antioxidant effectmay be observed, resulting in a decrease in the tendency of thecompounded oil to form sludge on oxidation. At somewhat highertemperatures, however, metallic naphthenates such as copper naphthenatemay have exactly the opposite effect. We have found, for example, that,copper naphthenate will actually increase sludge formation at atemperature of 310 F. when compounded'with a well known Pennsylvaniamotor oil of SAE 20 .grade. At still higher temperatures, of say from350 to 600 F. or even higher, naphthenates tend to exert a pro-oxidantefiect on petroleum oils, so strong as to cause the oil to oxidizefairly completely and leave a minimum of residue.

Since these metallic naphthenates in general do have such a pro-oxidanteffect, it has been suggested that certain naphthenates, such asaluminum naphthenate and calcium naphthenate, be used asanti-ring-sticking agents for lubricants, especially lubricants intendedfor use in Diesel and other heavy-duty internal combustion engines.

We have found, however, that nickel naphthenate, the use of which forthe purpose indicated has not to our knowledge been suggested by anyprior worker in the art, is exceptionally useful and advantageous, whenincorporated in petroleum lubricatng oils intended for use in internalcombustion engines, in improving the crankcases of internal combustionengines or otherwise harming the oil'.

Not only have we found that far smaller amounts of nickel naphthenateare necessary for incorporation in lubricating oils in order, to give adesired degree of improvement than is true of other naphthenates, but wehave also found that nickel naphthenate is effective in producingimprovement of certain highly refined oils of the character set forthhereinabove, the upper cylinder performance characteristics and rinsticking tendencies of which are not substantially improved by theincorporation therein of other naphthenates, such as aluminumnaphthenate.

In its preferred embodiment, therefore our invention comprises alubricant for internal combustion engines, particularly of theheavy-duty type (Diesel and aircraft engines), comprising a majoramountof a highly refined oil, such as an oil obtained from aPennsylvania crude or equivalent thereto, having a high viscosity-indexand a high inherent stability, and having incor-' porated therein asmall amount of nickel naphthenate. The oil base is referably adistillate oil, although residual stocks may be employed when desired.

We have found, however, that the use of nickel naphthenate is alsoadvantageous with respect to other types of oils andto the lubricationof internal combustion engines generally, and therefore our invention ina broader aspect also comprehends lubricants comprising variouspetroleum lubricating oils of the grades commonly used for all types'ofinternal combustion engines and having incorporated therein smallamounts of nickel naphthenate.

Ordinarily the amount of nickel naphthenate thus employed will run from0.05 to 2.0 per cent by weight of the lubricating oil base, the preciseamount depending upon the characteristics of the oil and the severity ofthe conditions to which the oil may be expected to be subjected.However, we have found that out of a large number of compounded oilstested, the best results were achieved with respect to analuminum-chloriderefined, non-residual Pennsylvania lubricating oil, ofSAE 10 or 20 grade, containing 0.2 per cent of nickel naphthenate. Thisapplies to Diesel-type engines primarily; for other engines, oils ofdifferent viscosities may-be used.

This particular compounded oil has been found to be exceptionallyadvantageous and desirable. It has been subjected to a'large number oftests of different types, all indicative of the performance of thetested lubricant when used in internal combustion engines, and theresults of such tests uniformly show improvement over the use of theuncompounded oil alone, as well as over the use of other oils whencompounded naphthenate are effective in preventing ringsticking andpermitting freedom from deposition] of undesirable solids in internalcombustion en gines because of a detergent action," it being p tulatedthat suchan agent assists in washing away or preventing the accumulationof deposits rather than by virtue of any action tending to prevent theinitial formation of mate: rials which if accumulated would form suchde-i posits. While we do not desire to limit our invention to anyparticular theory, nevertheless we are not in accord with the foregoingtheory of detergent action and believe rather that the action of nickelnaphthenate in the lubricant composition of our invention is primarilydue to the'prevention in the first instance of any tendency to formgummy or lacquer-like residues. A detergent action may be incidental.

In support of our conclusions in this respect, we' desire to refer tothe results obtained in certain tests in which small strips of aluminum,coated with 20 per cent solutions in hexane of oils and compounded oilscontaining naphthenates were exposed to a temperature of 625 F. for 30minutes in a gas-fired oven. Following such exposure, the strips wereexamined for staining as an evidence of formation of gum or lacquer-likeresidues. A highly refined, paraffinic oil, when subjected to this test,produced abad stain on the testing strips, indicating a substantialdeposit of lacquer-like material. The same oil, when compounded with 0.5per cent of aluminum naphthenate, showed no improvement. The same oilwhen compounded with 0.5 per cent of calcium naphthenate showed only asight improvement, but staining was still evident. However, when thesame oil was compounded with 0.5 per cent of nickel naphthenate andsubjected tothe foregoing test, no stain whatsoever was evident, themetal strips being clean and bright after the test.

The lacquer and gum deposit or stains produced in the foregoing testsappear to be analogous to similar deposits formed on the piston ringsand grooves during the operation of internal combustion engines andleading to ring-sticking. It appears likely that the eflicacy of nickelnaphthenate in preventing the formation of lacquerlike and gummydeposits in these tests is strictly analogous tothe effect of nickelnaphthenate in preventing ring-sticking and deposition of gum andlacquer-like deposits on the pistons in engine tests, possibly onaccount of an acceleration of oxidation of unvolatilized portions of theoil to the point of complete oxidation, thereby preventing the formationof intermediate products of oxidation of gum or lacquer-like nature.

We have carried out a number of engine tests for the purpose ofcomparing the compounded oils of our invention with uncompounded oilsand with oils compounded in the manner and according to the teachings ofthe prior art, with results uniformly indicating the superiority of thecompounded oils of our invention.

In one group of engine tests, no fixed ring clearance was observed, somevariation in the side clearance of the rings in the grooves(corresponding to manufacturing and replacement tolerances allowed bythe engine manufacturer) being characteristic of the tests. This groupof tests included individual tests covering 25 hour periods and 50 hourperiods, respectively. I

The data from the 25-hour tests in this group indicated clearly theeffectiveness of 0.2 per cent of nickel naphthenate, when added to ahighly refined oil, in reducing ring-sticking, carbon and sludgedeposition and in preventing lacquering of the piston surfaces. On theother hand, the average results of these 25-hour tests indicated noimprovement in engine performance resulting ing of the ring skirt werealso lower for the compounded oil, and 'tests indicating the physicalcharacteristics of the used oils after test showed a substantialimprovement in quality with respect td'the compounded oil, in comparisonwith the uncompounded oil alone. These tests also indicated asubstantial improvement in favor of the aforesaid compounded oil incomparison with an oil obtained from Coastal crude containingapproximately 1.44 per cent of aluminum naphthenate.

One criticism which has been directed to the testing data obtained inreference to ring-sticking has been to the effect that certainanti-ringsticking agents may owe their effectiveness to increased wearrather than to any inherent tend ency to prevent formation of depositsknown to cause ring-sticking. With this in mind, a second group of testswas formed .in which an effort was made to eliminate, as far aspossible, the effect of variation in ring clearance. In these tests theengine was disassembled and inspected at 25 hour intervals and anyeffect on ring-sticking produced by variation in ring clearance waseliminated by adjusting the side clearance in the grooves to a fixedvalue of 0.0015 inch around the circumierence of each ring before eachtesting period. The results of this group of tests conformed to those ofthe previously mentioned group of tests, and demonstrated the markedsuperiority of an oil composition comprising analuminum-chloride-refined Pennsylvania distillate oil compounded with0.2 per cent of nickel naphthenate. This compounded oil caused lessring-sticking in 100 hours of testing than was caused by the oil. alonein a 75 hour test period. Sludge deposition in the ring grooves andlacquering of the piston surfaces were also considerably lower in thecase of the compounded oil for equivalent testing periods, and anexamination of the used oils was also very much in. favor of thecompounded oil.

In-this connection it may be noted, without attempting to pass any finalopinion upon the effect of engine wear in the presence of metallicnaphthenates, that there is ample theoretical reason for believing thatnickel naphthenate has a far smaller tendency to promote wear thanaluminum napthenate, which has heretofore been regarded as among thebest of the naphthenates for the particular problem with which we areconcerned. Aluminum oxide (corundum), representing the ash produced byoxidation of alu-' minum naphthenate, is a much harder and more abrasivematerial than nickel oxide, which may be produced by the oxidation ofnickel naphthenate. On this basis alone, it is reasonable to In additionto the foregoing tests,- we have carried out competitive tests on anumber of competitive oils which are now in common use for thelubrication of Diesel engines and which have been recommended by one ofthe manufacturers of .these engines as superior Diesel engine oils.Examination of these oils shows that they are all low-viscosity Coastaloils compounded with aluminum or calcium soaps in amounts varying from0.5 to 1.5 per cent. All of these oils proved to be definitely inferiorto our preferred composition consisting of an aluminumchloride-refinedPennsylvania. distillate oil containing 0.2 per cent of nickelnaphthenate.

It should be observed that while we believe that we are the first tosuggest and demonstrate the remarkable effectiveness of nickelnaphthenate as an addition agent in the compounding of oils for thepurposes indicated, we do not claim that oils containing nickelnaphthenate alone, particularly the more highly refined oils, areespecially eifective in meeting specific bearingcorrosion problems whenencountered at high temperatures. However, a combination of nickelnaphthenate and certain types of alkylated phenols has been found to beespecially advantageous for this purpose. Oils containing such acombination of addition agents are described and claimed in thecopending application of Oliver L. Brandes, filed concurrently herewith,Serial No. 251,416, now issued as Patent 2,202,826, of June 4, 1940, andconstitute a specific improvement in the generic invention set forthherein.

While we have described our invention hereinabove with respect tovarious specific details and embodiments and particularly with referenceto a preferred specific embodiment, it will be understood by thoseskilled in the art that our invention in its broadest aspect is notlimited to such details, but may be variously practiced and embodiedwithin the scope of the appended claims.

naphthenate.

3. An improved lubricant for use in internal I combustion engines,comprising a major amount of a highly refinedand highly parafilnicpetroleum lubricating oil, having a high viscosity index, and havingincorporated therein a small amount, less than 2 per cent by weight, ofnickel naphthenate.

4. The method of reducing ring-sticking tendencies in an internalcombustion engine which comprises supplying to such engine, as alubricant therefor, a petroleumlubricating oil having incorporatedtherein a small amount of nickel naphthenate. Y

NORBERT F. TOUSSAINT. HANNIBAL J. R. GASP ARI. HENRY A. AMBROSE.

